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Optical and fundamental band gaps disparity in transparent conducting oxides: new findings for the [Formula: see text] and [Formula: see text] systems.
J Phys Condens Matter ; 29(8): 085501, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28060770
ABSTRACT
The optical band gap, extracted from absorption measurements, defines the figure of merit for transparent conducting oxides (TCOs). In many oxides, such as [Formula see text] or [Formula see text], inversion symmetry introduces a selection rule that blocks transitions from the valence-band maximum to the conduction-band minimum. This raises the absorption threshold and enlarges the optical gap relative to the fundamental band gap. Here, we present density-functional computations identifying two optical gaps, either of which can be detected, depending on the optical light intensity. Under strong illumination, weak transitions from [Formula see text]-points near the valence-band maximum contribute significantly to the absorption spectrum and define an optical gap matching the fundamental gap. Low optical intensities by contrast give prominence to the large optical gap determined by the selection rule. While experimental conditions have favored observation of the former optical gap in [Formula see text], in contrast, absorption measurements in [Formula see text] have focused on the latter. Our findings explain the disparity between the optical and fundamental gaps in bixbyite [Formula see text] and predict that, measured under low illumination, the optical gap for rutile [Formula see text] will increase, from 3.60 eV to 4.34 eV.

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Texto completo: Disponível Coleções: Bases de dados internacionais Base de dados: MEDLINE Aspecto clínico: Predição / Prognóstico Idioma: Inglês Revista: J Phys Condens Matter Assunto da revista: Biofísica Ano de publicação: 2017 Tipo de documento: Artigo País de afiliação: Brasil